Apparatus for restricting rotational moment about a longitudinal axis of SMT connectors

ABSTRACT

An electrical connector includes a first connector body having an interlocking feature extending therefrom. The interlocking feature interlocks the first connector body with a complimentary interlocking feature extending from an adjacent second connector body to distribute a lateral force on either the first or second connector bodies across the adjacent connector body thereby reducing a rotational moment at a base of each electrical connector connected to a printed circuit board (PCB).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/683,512, filed Mar. 8, 2007, the contents of which are incorporatedherein in their entirety.

TRADEMARKS

IBM® is a registered trademark of International Business MachinesCorporation, Armonk, N.Y., U.S.A. Other names used herein may beregistered trademarks, trademarks or product names of InternationalBusiness Machines Corporation or other companies.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for restricting arotational moment about a longitudinal axis of surface-mount (SMT)connectors, and particularly to a method and apparatus for restrictingthe rotational moment about the longitudinal axis of SMT DIMM Socketsand other SMT connectors.

2. Description of Background

In computer systems such as personal computers, a socket is referred toas an electrical connector generally mounted on a motherboard (mainboard) in order to connect extension boards such as extended interfaceboards for peripheral devices or extended memory boards to themotherboard. The motherboard and extension boards can be electricallyconnected by plugging the extension boards into the electricalconnector.

The structure of a common electrical connector will be described herewith the example of an electrical connector used to connect an extensionmemory module (hereinafter, “module”) referred to as a DIMM (dualin-line memory module) as illustrated in FIGS. 1 and 2. This modulecorresponds to the extension board described above.

A dual in-line memory module (DIMM) is more and more popular for use inthe present PC industry, and thus uses a DIMM socket connector mountedon the motherboard for mechanical and electrical interconnect of thecorresponding DIMM therein for signal transmission between themotherboard and the DIMM. A main feature of the typical DIMM connectoras illustrated in FIGS. 1 and 2 is that the DIMM connector 10 includesgenerally a pair of latch/eject members 12 at its two opposite ends sothat such DIMM may not only be properly retained in the DIMM connector10 without possibility of inadvertent withdrawal by vibration orexternal impact, but also easily ejected from the DIMM connector 10 byrotational movement of the latch/eject member 12.

With more of the industry moving to SMT (Surface Mount Technology)connectors due to PCB wiring density, path length, and electrical signalintegrity concerns, new mechanical requirements emerge due to thedelicate SMT interface, compared to the more mechanically robustcompliant pin and pin-through-hole interfaces in previous applications.This disclosure addresses the forces and strains incurred at the SMTsolder joint and pad interface due to rotation about the long axis of anSMT DIMM socket or housing 14, for example, as well as the possibilityof pad delamination at the card surface, by minimizing the overallrotation about the longitudinal axis of the SMT DIMM socket, asillustrated in FIG. 2.

Rotation about the longitudinal axis of the SMT DIMM socket 14 is causedby a number of factors. One factor is the amount and location of thecenter of mass of the DIMM module (not shown). The module acts as acantilevered beam when assembled into the socket 14, and, where shock,vibration, and dead load effects can all contribute to moments beingapplied to the DIMM connector 10, particularly when the DIMM module isplugged parallel to the ground and perpendicular to a motherboard 16 onwhich the DIMM connector 10 is surface mounted thereto. Another factoris due to the design of the connector 10 itself, allowing rotation ofthe DIMM module upon insertion. The traditional DIMM socket allowsapproximately 10 degrees of rotation centered about a perpendicularplane to a printed circuit board (PCB) surface defined by themotherboard 16. This allowable rotation, coupled with the high insertionforces required to mate the interface between the DIMM module and thesocket, results in a high lateral load forming a torsional moment aboutthe longitudinal axis of the connector inducing an undesirable shearstress to the SMT joint and PCB pad, regardless of orientation of themodule and connector with respect to gravity. This stress to the SMTjoints, as well as the SMT pad, creates a reliability concern, and thepossibility of pad delamination.

Previous designs were mechanically anchored to the PCB via thepin-through-hole or compliant pin nature of the PCB leads, as discussedabove which provided a larger reaction force to the lateral shear andtorsional moments than the present SMT joints provide. With the presentsurface-mount design, the reaction forces are carried through the SMTjoints and PWB solder pads, which are not as robust as pin-in-holeconnections to withstand such forces, and pose a reliability concern.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of an apparatus for supporting atleast one electrical connector body. The apparatus includes a firstconnector body having an interlocking feature extending therefrom. Theinterlocking feature interlocks the first connector body with acomplimentary electrical connector which includes a first connector bodyhaving an interlocking feature extending therefrom. The interlockingfeature interlocks the first connector body with a complimentaryinterlocking feature extending from an adjacent second connector body todistribute a lateral force on either the first or second connectorbodies across the adjacent connector body thereby reducing a rotationalmoment at a base of each electrical connector connected to a printedcircuit board (PCB).

In another exemplary embodiment, a system includes: a motherboard; aplurality of electrical connectors surface mounted to the motherboard,each electrical connector including a connector body configured toreceive and electrically connect an electrical module; and aninterlocking feature extending from each electrical connector. Theinterlocking feature interlocks a first connector body with acomplimentary interlocking feature extending from an adjacent secondconnector body to distribute a lateral force on either the first orsecond connector bodies across the adjacent connector body therebyreducing a rotational moment at a base of each electrical connectorconnected to the motherboard.

In still another exemplary embodiment, a method of constraining rotationof electrical connectors about a longitudinal axis thereof at aninterface of a motherboard to which it is surface mounted is disclosed.The method includes: configuring each electrical connector including aconnector body to receive and electrically connect an electrical module;and extending an interlocking feature from each electrical connector.The interlocking feature interlocks a first connector body with acomplimentary interlocking feature extending from an adjacent secondconnector body to distribute a lateral force on either the first orsecond connector bodies across the adjacent connector body therebyreducing a rotational moment at a base of each electrical connectorconnected to the motherboard.

The present invention addresses the over-stress of the SMT joint due toconnector rotation by restricting rotation of the DIMM connectors on thecircuit card via rigid member braces between the connectors.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with advantagesand features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a perspective view of a conventional DIMM connector;

FIG. 2 illustrates an elevation end view of the DIMM connector of FIG. 1surface mounted to a PCB surface of a motherboard;

FIG. 3 illustrates an elevation end view of the DIMM connector of FIG. 1surface mounted to a PCB surface of a motherboard with an exemplaryembodiment of a lateral constraint member disposed on either side of theDIMM connector;

FIG. 4 illustrates a top plan view of DIMM connectors surface mounted tothe PCB surface of the motherboard with an exemplary embodiment oflateral constraint members having interstitial interlocking rigidfeatures;

FIG. 5 illustrates an elevation end view of two of the DIMM connectorsof FIG. 4 with the exemplary embodiment of rigid lateral constraintmembers extending therefrom and having interstitial interlockingfeatures therebetween;

FIG. 6 illustrates a top plan view of an exemplary embodiment of lateralconstraint members between two DIMM connectors (case 1) and four DIMMconnectors (case 2); and

FIG. 7 illustrates a table of results of finite element modeling forcases 1 and 2 of FIG. 6 showing that constraining the rotation of theDIMM connectors via rigid-body members contacting/joining the DIMMconnector housings greatly decreases the allowable rotation of theconnector and thus the rotational moment and shear stress of the SMTjoints and PCB pads.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings in greater detail, the structure of a commonelectrical connector will be described here with the example of anelectrical connector used to connect an extension memory module(hereinafter, “module”) referred to as a DIMM (dual in-line memorymodule). This module corresponds to the extension board described above.

FIG. 3 is a schematic elevation end view illustrating the structure ofan exemplary embodiment of an electrical connector assembly 100 for aDIMM (not shown) according to the present invention. The electricalconnector assembly 100 is an electrical connector which is used indesktop personal computers, for example. In FIG. 3, the connectorassembly 100 is defined by a housing 140 for housing a respective module(not shown). The modules are arranged in several rows (e.g., two rows inFIG. 5) on a PCB or motherboard 160. The user inserts a module (notshown) in the housing 140, allowing memory to be added on. When thehousing 140 is arranged standing up on the motherboard 160, asillustrated in FIG. 3, the module is held perpendicular to themotherboard 160. In order to counteract a lateral force indicated witharrow 162 when inserting a module (not shown) for electrical connectionwith the connector assembly 100, a reaction force indicated with arrow164 may be applied to preserve the integrity of the SMT joint interfacebetween the connector assembly 100 and the motherboard 160. The reactionforce 164 is applied by exemplary interstitial braces 170 acting asrigid lateral constraint members disposed on either side of eachconnector assembly 100. The reaction force 164 reduces a rotationalmoment 166 about a longitudinal axis defined by the connector 100assembly at the SMT joint interface between the connector 100 assemblyand the motherboard 160 when the lateral force 162 is applied.

Still referring to FIG. 3, it will be recognized by those skilled in theart that in the force diagram thereof, the opposite (reverse) would betrue as well, as the interstitial braces 170 as rigid members wouldcontact both sides of the DIMM connector assembly 100. The forcedepicted in FIG. 3 would be induced by either a non-perpendicularplugging (which is allowed in the connector design), or by gravitationalforce if the overall assembly was rotated 90 degrees, as is typical insystem applications.

The interstitial braces 170 can be applied to the connector assembly 100in various ways, as described hereinbelow. In an exemplary embodiment asillustrated in FIG. 3, the interstitial braces 170 are defined byprotruding features extending from the connector assembly 100. Theprotruding features 170 may be separate or integral with the housing 140defining the connector assembly 100. The protruding features 170interlock with complimentary protruding features 170 extending from anadjacent connector assembly 100 to form compound connector assemblies,as illustrated in FIGS. 4-6.

Referring now to FIG. 5, the protruding features 170 on the connectorassembly 100 include interlocking features 172, 174 which interlock withrespective complimentary configured interlocking features 172, 174extending from an adjacent connector assembly. In other words, eachconnector assembly 100 includes a tongue 172 extending on one side and agrooved piece 174 extending from an opposite side. In this manner, atongue 172 extending from one connector assembly may interlock with agroove 176 of the grooved piece 174 extending from an adjacent connectorassembly providing an interstitial brace 170 between the joined twoadjacent connector assemblies. Possible geometries contemplated for thecomplimentary interlocking features 172, 174 include a tongue-and-grooveconfiguration or dove-tail configuration, for example, but is notlimited thereto.

Referring now to FIG. 4, the ganging of connector assemblies 100provides an assembly 200 of a given number of connector assemblies 100as one rigid entity and provides a more stable geometry and minimizesthe rotation of any one connector assembly 100 in the gang. Theinterlocking features 170 are not limited to being located at the endsof the connector assemblies, as illustrated in FIG. 6, but can be placedat multiple locations along a body defining each connector assembly 100,as determined by the amount of reaction force 164 required to counteractthe lateral force 162 (FIG. 3). For example, FIG. 4 illustrates two gangassemblies 200. One gang assembly 200 has the interlocking features 170located at ends of the connector assemblies 100 while the other gangassembly 200 has the interlocking features 170 located at opposing endsand a middle portion of each connector assembly 100. Thus, theinterlocking features 172, 174 may have various configurations and maybe disposed along an entire length, at ends, or at ends and midsectionsof a connector assembly 100.

The interlocking features 172, 174 can also be designed such that theydo not run the entire height of the connector, as illustrated in FIGS. 3and 5, such that a volume is allowed for component placement below thefeatures on PCB 160. Although it is desirable, it not necessary, toleave a volume beneath the interlocking sections to allow for componentplacement or increased air flow between PCB 160 and a bottom surfacedefining the interlocking features 172, 174 extending from eachconnector assembly 100.

The geometry of the interlocking features 172, 174 is not specific, asthey can be designed for ease of disassembly/rework of the individualconnector assemblies 100 in the ganged assembly 200, or other factorsspecific to the given application. One advantage to a vertically-lockingdovetail/interlock (not shown in FIG. 5) is that it allows for verticalremoval of the DIMM connector assemblies 100 in rework. In other words,it is preferable that the interlocking features 172, 174 of FIG. 5 berotated 90 degrees so that they interlock vertically to allow forpotential removal of the connector assembly 100 from a ganged assembly200. The reworkability of this design is an advantage over one largeconnector assembly with multiple slots resembling the ganged assembly200. Instead of pulling off an entire large connector assembly withmultiple slots in rework, an individual isolated connector assembly 100can be removed without disturbing the adjacent connector assemblies 100of a ganged assembly 200. It will be recognized by those skilled in thepertinent art that this option for orientation, as well as the onedepicted in FIG. 5, is contemplated for all embodiments.

Still referring to FIG. 4, it will be recognized that havinginterlocking connector assemblies 100 limits the pitch of the connectors(e.g., limits the number of connector assemblies per unit area).Therefore, in alternative exemplary embodiments, the interlockinginterstitial braces may accept a secondary piece, the secondary piecebeing of various lengths to accommodate various pitches. Thisalternative exemplary embodiment is specifically valuable to lockadjacent connector assemblies 100 after they have been installed ontothe PCB 160.

For example, referring to the lower gang assembly 200 of FIG. 4, ifthere are only two connector assemblies 100 interlocked together(although three are shown in FIG. 4), in addition to the first andsecond interlocking features 172, 174 disposed at each opposing end ofthe connector assembly, respectively, there is at least a thirdinterlocking feature 178 in a middle portion of the connector assembly100. This third interlocking feature 178 is configured to accommodateother connector assemblies of various pitches. One method of adjustingthe connector pitch is by a variable length linkage between lockingfeatures on the connector. This could be a shaft in sleeve structurewhich provides a telescopic action to the linkage and still provides amoment couple to the connector locking features.

Referring to FIGS. 6 and 7, it has been proven via finite elementmodeling that constraining the rotation of the DIMM connector assemblies100 via rigid-body members (e.g., interstitial braces 170)contacting/joining the housings thereof greatly decreases the allowablerotation of the connector assembly 100 and thus the rotational momentand shear stress of the SMT joints and PCB pads. Material properties,dimensions, and tolerances of the body/housing interface are applicationdependent.

Case 1 of FIGS. 6 and 7 illustrates a situation where interstitialbraces 170 are disposed at ends and between alternate pairs of DIMMconnector assemblies 100, having a 7 mm length. Case 2 of FIGS. 6 and 7illustrates a situation where interstitial braces 170 are disposedbetween a group of four DIMM connector assemblies 100 and at endsthereof. The DIMM connector assemblies 100 were 3, 4, 5, 6 and 7 mm inlength and using anisotropic material data sets for all materials in thefinite element model. In both cases 1 and 2, the allowable pad stress is44-65 psi.

From the above described exemplary embodiments, the following attributesof the present invention are disclosed. A connector assembly includes abody having interlocking features, wherein the interlocking featuresinterlock one connector body to an adjacent connector body. In thismanner a lateral force applied thereto is distributed across theadjacent connectors thereby reducing the rotational moment at the baseof each connector. The interlocking features may be placed in multiplelocations. More and more connector bodies can be interlocked dependingon the expected amount of lateral force (the more force expected, themore interlocked connectors, thereby distributing the rotational momentacross all interlocked connectors.

While the preferred embodiment to the invention has been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. An electrical connector comprising: a first connector body having aninterlocking feature extending therefrom, wherein the interlockingfeature rigidly interlocks the first connector body with a complimentaryinterlocking feature extending from an adjacent second connector body todistribute a lateral force on either the first or second connectorbodies across a longitudinal side of the adjacent connector body therebyreducing a rotational moment at a base of each electrical connectorconnected to a printed circuit board (PCB), and the interlockingfeatures are configured to separate the first connector body from theadjacent second connector body and maintain a space therebetween.
 2. Theelectrical connector of claim 1, wherein the interlocking features ofthe first and second connector bodies are disposed in multiple locationsalong a length defining the longitudinal sides of the first and secondconnector bodies.
 3. The electrical connector of claim 2, wherein theinterlocking features are disposed at least at opposing ends or middleportions along the longitudinal sides defining each of the first andsecond connector bodies.
 4. The electrical connector of claim 1, whereinthe interlocking features include a dovetail or tongue-and-grooveinterlock feature.
 5. The electrical connector of claim 4, wherein theinterlocking connector bodies interlock vertically, to facilitateremoval of at least one of the first and second connector bodies.
 6. Theelectrical connector of claim 1, wherein more than two connector bodiescan be interlocked depending on an expected amount of lateral force,thereby distributing the rotational moment across all interlockedconnectors, and wherein if two connectors are interlocked together, inaddition to first and second interlocking features at each end of thetwo connectors, respectively, there is at least a third interlockingfeature in a middle of the two connectors configured to accommodateanother adjacent connector of a same or different pitch of the other twoconnectors.
 7. The electrical connector of claim 1, wherein theinterlocking features are configured having a volume therebeneath andabove the PCB allowing for component placement or increased air flow. 8.A system comprising: a motherboard; a plurality of electrical connectorssurface mounted to the motherboard, each electrical connector includinga connector body configured to receive and electrically connect anelectrical module; and an interlocking feature extending from eachelectrical connector, wherein the interlocking feature rigidlyinterlocks a first connector body with a complimentary interlockingfeature extending from an adjacent second connector body to distribute alateral force on either the first or second connector bodies across alongitudinal side of the adjacent connector body thereby reducing arotational moment at a base of each electrical connector connected tothe motherboard, and the interlocking features are configured toseparate the first connector body from the adjacent second connectorbody and maintain a space therebetween.
 9. The system of claim 8,wherein the interlocking features of the first and second connectorbodies are disposed in multiple locations along a length defining thelongitudinal sides of the first and second connector bodies.
 10. Thesystem of claim 9, wherein the interlocking features are disposed atleast at opposing ends or middle portions along the longitudinal sidesdefining each of the first and second connector bodies.
 11. The systemof claim 9, wherein the interlocking features are a locking dovetailinterlock feature.
 12. The system of claim 11, wherein the interlockingconnector bodies interlock vertically, to facilitate removal of at leastone of the first and second connector bodies.
 13. The system of claim 9,wherein more than two connector bodies can be interlocked depending onan expected amount of lateral force, thereby distributing the rotationalmoment across all interlocked connectors, and wherein if two connectorsare interlocked together, in addition to first and second interlockingfeatures at each end of the two connectors, respectively, there is atleast a third interlocking feature in a middle of the two connectorsconfigured to accommodate another adjacent connector of a same ordifferent pitch of the other two connectors.
 14. The system of claim 1,wherein the interlocking features are configured having a volumetherebeneath and above the motherboard allowing for component placementor increased air flow.